1. Centre for Aviation, Transport and the Environment, School of Science and the Environment, Manchester Metropolitan University, Chester Street, Manchester M1 5GD, U.K.
2. British Airways PLC, Waterside (HBA3), P.O. Box 365, Harmondsworth UB7 0GB, U.K.
3. Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, U.K.